Date:   Thu, 28 Sep 2017 10:33:18 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Oleksandr Shamray <oleksandrs@...lanox.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        openbmc@...ts.ozlabs.org, Joel Stanley <joel@....id.au>,
        Jiri Pirko <jiri@...nulli.us>,
        Tobias Klauser <tklauser@...tanz.ch>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        mec@...ut.net, Vadim Pasternak <vadimp@...lanox.com>,
        system-sw-low-level@...lanox.com, Rob Herring <robh+dt@...nel.org>,
        openocd-devel-owner@...ts.sourceforge.net,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [patch v9 0/4] JTAG driver introduction

Hi Oleksandr,

[My attention was drawn by https://lwn.net/Articles/734440/]
[CC linux-spi, which was never included, while linux-serial was]

On Thu, Sep 21, 2017 at 11:25 AM, Oleksandr Shamray
<oleksandrs@...lanox.com> wrote:
> When a need raise up to use JTAG interface for system's devices
> programming or CPU debugging, usually the user layer
> application implements jtag protocol by bit-bang or using a
> proprietary connection to vendor hardware.
> This method can be slow and not generic.
>
> We propose to implement general JTAG interface and infrastructure
> to communicate with user layer application. In such way, we can
> have the standard JTAG interface core part and separation from
> specific HW implementation.
> This allow new capability to debug the CPU or program system's
> device via BMC without additional devices nor cost.
>
> This patch purpose is to add JTAG master core infrastructure by
> defining new JTAG class and provide generic JTAG interface
> to allow hardware specific drivers to connect this interface.
> This will enable all JTAG drivers to use the common interface
> part and will have separate for hardware implementation.
>
> The JTAG (Joint Test Action Group) core driver provides minimal generic
> JTAG interface, which can be used by hardware specific JTAG master
> controllers. By providing common interface for the JTAG controllers,
> user space device programing is hardware independent.
>
> Modern SoC which in use for embedded system' equipped with
> internal JTAG master interface.
> This interface is used for programming and debugging system's
> hardware components, like CPLD, FPGA, CPU, voltage and
> industrial controllers.
> Firmware for such devices can be upgraded through JTAG interface during
> Runtime. The JTAG standard support for multiple devices programming,
> is in case their lines are daisy-chained together.
>
> For example, systems which equipped with host CPU, BMC SoC or/and
> number of programmable devices are capable to connect a pin and
> select system components dynamically for programming and debugging,
> This is using by the BMC which is equipped with internal SoC master
> controller.
> For example:
>
> BMC JTAG master --> pin selected to CPLDs chain for programming (filed
> upgrade, production)
> BMC JTAG master --> pin selected to voltage monitors for programming
> (field upgrade, production)
> BMC JTAG master --> pin selected to host CPU (on-site debugging
> and developers debugging)
>
> For example, we can have application in user space which using calls
> to JTAG driver executes CPLD programming directly from SVF file
>
> The JTAG standard (IEEE 1149.1) defines the next connector pins:
> - TDI (Test Data In);
> - TDO (Test Data Out);
> - TCK (Test Clock);
> - TMS (Test Mode Select);
> - TRST (Test Reset) (Optional);
>
> The SoC equipped with JTAG master controller, performs
> device programming on command or vector level. For example
> a file in a standard SVF (Serial Vector Format) that contains
> boundary scan vectors, can be used by sending each vector
> to the JTAG interface and the JTAG controller will execute
> the programming.
>
> Initial version provides the system calls set for:
> - SIR (Scan Instruction Register, IEEE 1149.1 Data Register scan);
> - SDR (Scan Data Register, IEEE 1149.1 Instruction Register scan);
> - RUNTEST (Forces the IEEE 1149.1 bus to a run state for a specified
>   number of clocks.
>
> SoC which are not equipped with JTAG master interface, can be built
> on top of JTAG core driver infrastructure, by applying bit-banging of
> TDI, TDO, TCK and TMS pins within the hardware specific driver.

Or by using an SPI master?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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